1. Technical Field
The present invention relates to a lash adjuster.
2. Related Art
A conventional lash adjuster includes a bottomed cylindrical body fixed to a cylinder head of an internal combustion engine and a plunger which is inserted into the body so that the plunger is movable up and down. The plunger has an upper end supporting a rocker arm. The plunger further has a peripheral wall formed with an oil passage hole and a bottom wall formed with a valve hole. Hydraulic fluid, such as oil, supplied through an oil filler hole of the cylinder head is stored in a low-pressure chamber in the plunger through the oil passage hole and also supplied through the valve hole into the body thereby to fill the body. A high-pressure chamber is defined by dividing an interior of the body by the bottom wall of the plunger. The plunger is moved up and down according to oil pressure in the high-pressure chamber. The hydraulic fluid in the low-pressure chamber in the plunger is drawn through the valve hole into the high-pressure chamber when the plunger is moved upward. In this case, there is a possibility that air entrainment may occur in the high-pressure chamber when the hydraulic fluid level is low in the low-pressure chamber.
In view of the aforementioned problem, the conventional art provides a lash adjuster provided with a cylindrical partitioning member inserted into the plunger. A space inside the partitioning member serves as a low-pressure chamber. An oil passage is formed between an inner periphery of the plunger and an outer periphery of the partitioning member. An oil passage end is located above the oil passage hole. As a result, a large amount of hydraulic fluid is supplied from the oil passage hole via the oil passage and the oil passage end into the low-pressure chamber. Since the hydraulic fluid level depends upon the oil passage end located above the oil passage hole, air entrainment can be prevented in the high-pressure chamber.
The oil passage is defined over an entire circumference of the partitioning member in the above-described conventional lash adjuster. This results in a problem that the hydraulic fluid has a high pressure loss when passing through the oil passage. When a radial passage width of the oil passage is increased for the purpose of improving a flow speed of hydraulic fluid, an inner diameter of the partitioning member is reduced in inverse proportion to the increase in the passage width. This results in a problem that a sufficient amount of hydraulic fluid cannot be ensured in the low-pressure chamber.